My thesis focuses on metamorphic phyllites from Peloponnesus, Greece that formed due to the African plate subducting underneath the Eurasian plate that has been in convergence since the late Mesozoic. The samples are from a specific metamorphic unit known as the Phyllite-Quartzite (PQ) unit that contains blueschist facies minerals. This unit is of interest because blueschist minerals form under high-pressure, low-temperature (HP-LT) conditions present in the subducting slab.
In this study, twelve thin sections from the Peloponnesus region were analyzed using the scanning electron microscope to determine the mineral and chemical compositions. Before each analysis, the SEM was standardized for specific minerals, chloritoid, chlorite, phengite, epidote, and glaucophane in twelve thin sections. The ultimate goal of this thesis is to investigate the thermobarometic conditions in which these rocks metamorphosed.
In order to understand the temperatures of how the rocks formed, six thin sections that contained both chlorites and chloritoids were assessed using the Mg-Fe exchange thermometer that was used in Vidal et al. (1999). Based on the calculated KDs values, the temperatures show formation between 350-600 oC. To comprehend the pressure gradient, the Si content of phengite of twelve samples show a minimum pressure of ~10 kbar. This pressure is of significance because a previous study by Theye and Seidal (1991) found pressure formation to be around 17 kbar.
This study is of interest for its implication for different possible formations for the PQ unit of Peloponnesus, Greece. This study addresses the behavior of blueschist minerals, which typically form under colder temperature conditions of 200-400oC and higher pressures ranging 4-17 kbar. The PQ unit was exhumed back to the surface through rollback extension from the subduction reaction.